For vehicles such as automobiles, due to advancement in technology of engine noise reduction, a road noise that results from a vibration input from a road surface during traveling of a vehicle has become increasingly apparent. As one of the reasons for this road noise, cavity resonance has been raised, and it occurs in a space within a tire that is sealed by the tire and a rim part of a vehicle wheel. This cavity resonance is generated when a standing wave having one wavelength equal to a perimeter of the space within the tire is generated by the vibration input from the road surface during traveling of the vehicle and then this standing wave causes a columnar resonance phenomenon in a particular frequency band (e.g., 180 Hz to 240 Hz).
As a method for reducing the above cavity resonance, a configuration that applies a Helmholtz resonant absorber has been proposed. For example, a configuration has been proposed in which plural auxiliary air chambers in Japanese Patent Publication No. 2003-326904(JP-A-2003-326904) are circumferentially formed in the rim part of the vehicle wheel and in which a hole that communicates with the space within the tire is provided for each of the auxiliary air chambers. In this configuration, a Helmholtz resonant absorber is constituted by the auxiliary air chambers and the holes, and it is thereby possible to reduce the cavity resonance that occurs in the space within the tire. The patent document: JP-A-2003-326904 suggests a method for shaping the auxiliary air chamber and the hole that includes the steps of: forming a vertical wall part that projects from an outer surface of the rim part during casting; bending the vertical wall part to form the auxiliary air chamber; and drilling the hole in the bent vertical wall part.